A bipolar battery is typically constructed by laminating a plurality of bipolar electrodes with a plurality of electrolyte layers through which ions move internally. The bipolar electrode comprises a layer-form collector, a positive electrode active material layer disposed on one surface of the collector, and a negative electrode active material layer disposed on another surface of the collector. The lamination is performed such that the positive electrode active material layer and the negative electrode active material layer oppose each other via the electrolyte layer.
In a laminated condition, the positive electrode active material layer and the negative electrode active material layer opposing each other via the electrolyte layer constitute a unit cell. In the bipolar battery, therefore, a plurality of unit cells are connected in series.
The unit cells vary in internal resistance, capacity, and so on due to factors arising during a manufacturing process. When variation exists among voltages apportioned to the unit cells, deterioration advances from a unit cell having a large voltage, and as a result, a lifespan of the entire bipolar battery shortens.
To extend the lifespan of the entire bipolar battery, therefore, the voltage of each unit cell is preferably measured, whereupon the voltage of each unit cell is adjusted on the basis of the measured voltage.
JP 2005-235428, published by the Japan Patent Office in 2005, teaches that in order to measure the voltage of each unit cell of a bipolar battery, a voltage detection terminal is to be attached to the collector of each unit cell so that a voltage can be extracted from each unit cell for measurement.